I've been working on a build to include an optical amp for a while, and put my parts list together before joining the forum. See if this helps you at all, it is the base nettop I'm planning on using and an amp I found.
ASRock 330 $255
MRA-F350 Alpine 5 ch 250W AMP $195
if you want to see the current list of what I'm considering it can be found here
Thanks for the heads up